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Die spacer thickness reproduction for central incisor crown fabrication with combined computer-aided design and 3D printing technology: an in vitro study. J Prosthet Dent 2015 May;113(5):398-404



Pubmed ID




Scopus ID

2-s2.0-84929513908 (requires institutional sign-in at Scopus site)   40 Citations


STATEMENT OF PROBLEM: The inability to control die spacer thickness has been reported. However, little information is available on the congruency between the computer-aided design parameters for die spacer thickness and the actual printout.

PURPOSE: The purpose of this study was to evaluate the accuracy and precision of the die spacer thickness achieved by combining computer-aided design and 3-dimensional printing technology.

MATERIAL AND METHODS: An ivorine maxillary central incisor was prepared for a ceramic crown. The prepared tooth was duplicated by using polyvinyl siloxane duplicating silicone, and 80 die-stone models were produced from Type IV dental stone. The dies were randomly divided into 5 groups with assigned die spacer thicknesses of 25 μm, 45 μm, 65 μm, 85 μm, and 105 μm (n=16). The printed resin copings, obtained from a printer (ProJet DP 3000; 3D Systems), were cemented onto their respective die-stone models with self-adhesive resin cement and stored at room temperature until sectioning into halves in a buccolingual direction. The internal gap was measured at 5 defined locations per side of the sectioned die. Images of the printed resin coping/die-stone model internal gap dimensions were obtained with an inverted bright field metallurgical microscope at ×100 magnification. The acquired digital image was calibrated, and measurements were made using image analysis software. Mixed models (α=.05) were used to evaluate accuracy. A false discovery rate at 5% was used to adjust for multiple testing. Coefficient of variation was used to determine the precision for each group and was evaluated statistically with the Wald test (α=.05).

RESULTS: The accuracy, expressed in terms of the mean differences between the prescribed die spacer thickness and the measured internal gap (standard deviation), was 50 μm (11) for the 25 μm group simulated die spacer thickness, 30 μm (10) for the 45 μm group, 15 μm (14) for the 65 μm group, 3 μm (23) for the 85 μm group, and -10 μm (32) for the 105 μm group. The precision mean of the measurements, expressed as a coefficient of variation, ranged between 14% and 33% for the 5 groups.

CONCLUSIONS: For the accuracy evaluation, statistically significant differences were found for all the groups, except the group of 85 μm. For the precision assessment, the coefficient of variation was above 10% for all groups, showing the printer's inability to reproduce the uniform internal gap within the same group.

Author List

Hoang LN, Thompson GA, Cho SH, Berzins DW, Ahn KW


Kwang Woo Ahn PhD Professor in the Institute for Health and Equity department at Medical College of Wisconsin
David Berzins BS,PhD Graduate Program Director for Dental Biomaterials in the General Dental Sciences/Dental Biomaterials department at Marquette University

MESH terms used to index this publication - Major topics in bold

Computer-Aided Design
Dental Marginal Adaptation
Dental Prosthesis Design
Image Processing, Computer-Assisted
Materials Testing
Printing, Three-Dimensional
Random Allocation
Resin Cements
Surface Properties
Tooth Preparation, Prosthodontic